• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.11
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• pp.1-8
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• 1997

A prediction model is proposed to describe the path loss in propagation environment of indoor microcell. This model includes the lineal corridor for line--of-sight(LOS) and T-shaped corridor for non-line-of-sight(NLOS). In computation of receiving power the ray tracing technique based on image method is utilized and also reflected waves bounced on the walls and ceilings are considered. To check validity of the computed resuls cross checks between the predicted and measured are being made, which shows a close agreement for LOS case whereas somewhat disagreement for NLOS case. UTD technique is incorporated with propagation path determination algorithm in the treatment of NLOS case.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.2
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• pp.15-22
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• 1996

This paper presents the generalized method of the prediction of the LOS propagating characteristics in an urban microcell by using theray tracing technique. Whereas the received power is calculated by the finite number of pths, 4~10, on an urban steet, the RMS delay spread is comuted by using the sufficient rays of convergence. To take into account the infinite number of paths the technique of the numbering scheme of image antennas was presented by using the rectangular pulse. As to this the existing restriction of the finitte number of paths was relaxed. based on the method of extending the number of paths and the canyon model the received power and RMS delay spread are computed and their differences according to the number of paths are compared at the frequencies of both 1GHz and 2GHz, respectively.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.2
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• pp.40-49
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• 1996

In this paper, we studied channel assignment and handover schemes for the indoor microcell systems. For efficient frequency spectrum reuse we proposed the high quality reassignment (HQR) scheme. Proposed HQR scheme tries to keep the reuse distances small by monitoring C/I of channels being used. To assign a channel for a new or handove call, the scheme checks C/I of all available channels. Then HQR assigns the channel that has C/I near the threshold value, A_TH. The scheme also checks C/I of ongoing calls and continuously reassigns a new channel when needed. It attempts handover not only when C/I gets below a handover threshold value, HO_TH, but also when C/I becomes above a high quality reassignment threshold, H_TH. The performance of the proposed HQR scheme was analyzed by a computer simulation configuraed. The performance of the scheme was also analyzed for various threshold values selected and the results are presented in this paper. The results show that HQR scheme perfomrs better than the scheme adopted for DECT.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.11
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• pp.78-87
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• 1996

in urban cross-roads with dense buildings, receiving power and delay spread were computed when doing these, we were able to develope codes to be executed in a very fast time by combining image method and algorithm for propagation paths compairing with ray launching technique. And receiving power and delay spread could be viewed in 3-dimensional picture by virtue of computing electric fields in arbitrary receiving point. For numerical computation, receiving power of wide and anrrow band and delay spread were computed, and extension method of ray numbers was facilitated for handling infinite number of rays.

• Journal of Korean Institute of Industrial Engineers
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• v.26 no.2
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• pp.155-164
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• 2000

Recently Fiber-optic Micro-cellular Wireless Network is considered to solve frequent handoffs and local traffic unbalance in microcellular systems. In this system, central station which is connected to several microcells by optical fiber manages the channels. We propose an efficient sectorization algorithm which dynamically clusters the microcells to minimize the blocked and handoff calls and to balance the traffic loads in each cell. The problem is formulated as an integer linear programming. The objective is to minimize the blocked and handoff calls. To solve this real time sectorization problem the Tabu Search is considered. In the tabu search intensification by Swap and Delete-then-Add (DTA) moves is implemented by short-term memory embodied by two tabu lists. Diversification is considered to investigate proper microcells to change their sectors. Computational results show that the proposed algorithm is highly effective. The solution is almost near the optimal solution and the computation time of the search is considerably reduced compared to the optimal procedure.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.4C
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• pp.388-397
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• 2002

We designed a SIMD-DSP/FPU that can efficiently improve multimedia processing performance when integrated into high-performance embedded microprocessors. We proposed partitioned architectures and new schemes for several functional units to reduce chip area. Sharing functional units reduces the area of FPU significantly. The proposed architecture is modeled in HDL and synthesized with a 0.35$\mu\textrm{m}$ standard cell library. The chip area is estimated to be about 100,000 equivalent gates. The designed unit can run at higher than 50MHz clock frequency of CPU core under the worst-case operating conditions.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.8
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• pp.10-19
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• 1997

In this paper, perfodrmance of matched-filter (MF) acquisition scheme is analyzed for a direct-sequence/code-division-multiple-access (DS/CDMA) system in a microcellular environment. Mean acquistion time is used as a performance measure. It is demonstrated that acquisition performance is enhanced using interference suppression filter in a Rician fading channel. To apply for multiuser environments, multiple access interference is considered in the performance analysis. From the numerical results, it is shown that mean acquistion time decreases with the increasing SNR/chip, and acquisition performance is improved as the number of taps of interference suppression filter. It is also shown that mean acquisition time increases with the number of users in the system, and acquistion performance is degraded as the icrease of narrowband interference bandwidth. The analysis in this paper can be applied to a DS/CDMA overlay environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.9
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• pp.2494-2504
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• 1996

This paper describes about the spread specturm radio wave propagation characteristics in urban microcells. The experiments are carried out with respect to the mean excess delay, the RMS delay spread, and the received maximum peak power in the two kinds of geogrphical areas, LOS area and N-LOS area, especially whose variations are observed while varying the transmission distance and tilting the transmitting antenna. The typical results obtained in pariticular urban sites in Seoul are 300-600 nsec of mean excess delay and about 75 nsec of averaged RMS delay spread for LOS area, and 270-280 nsec of mean excess delay and about 100 nsec for N-LOS area. With the transmitting antenna gilted, obsered in the experiments are increase in RMS delay spread as expected, but increase of the received power at N-LOS areas in particular.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.2201-2203
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• 2000

본 논문에서는 도심지 마이크로셀의 전파환경 특성을 예측하기 위한 무선 채널 파라미터 산출 코드를 구현하였다. 이를 위해 광선추적기법을 이용하여 전파가 겪게 되는 회절과 다중반사의 위치를 구한 다음 전장을 계산하였다. 광선추적기법의 구현시 경로 계산에 소요되는 시간의 단축을 위해 건물의 모든 모서리에서 발생되는 회절 이후의 광선추적을 먼저 수행하는 기법을 제안하였으며, 기존 방법의 결과와 동일하면서도 하나의 수신점에 대한 계산시간을 1/70 하로 단축하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.7A
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• pp.1144-1151
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• 2001

본 연구에서는 AOA(Angle of Arrival)와 TOA(Time of Arrival) 그리고 TDOA(Time Difference of Arrival)의 추정값을 이용한 위치 추정 기법들이 설명되고 분석된다. 이들 기법들을 다중경로 페이딩 (mutipath fading)과 shadowing을 갖는 마이크로셀 환경에 적용한다면, 빠르고 예측할 수 없는 신호 레벨의 변화로 인하여 이동체의 위치를 정확히 추정하는 것은 어렵다. 따라서 본 연구에서는 수신 신호 세기(RSS: Received Signal Strength) 이외에 이동체와 기지국간의 거리, 이동체의 이동방향, 이동체의 이전위치와 같은 부정확한 다수의 파라미터를 동시에 고려하는 퍼지 다기준 (multi-criteria) 의사 결정 방법을 이용하여 이동체의 위치를 결정하는 방법을 제안한다. 시뮬레이션을 통하여, 이동체의 방향과 속도의 영향을 분석한다.